Most efforts to understand the mechanisms and processes underlying speech perception have not examined how semantic knowledge is accessed during speech perception. The proposed research aims to investigate how meaning is accessed during spoken word comprehension using behavioral and eye-tracking methods and to develop a mechanistic theory of speech perception that incorporates activation of semantic representations. Proposed behavioral experiments test the effect of semantic neighborhood density on word recognition and compare the importance of rare and frequent semantic features in determining semantic similarity. Proposed eye tracking experiments provide fine-grained convergent data that will further elucidate how semantic knowledge is accessed from spoken input. A proposed computational model will integrate semantic knowledge in speech processing to account for the behavioral and eye tracking results and to make novel predictions. [unreadable] [unreadable] [unreadable]